Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $151.36   11.481%   $168.7376   $168.74   $168.75   $168.70  
  Purchase #2 $7.46   4.577%   $7.8014   $7.80   $7.80   $7.80  
  Purchase #3 $50.75   6.818%   $54.2101   $54.21   $54.20   $54.20  
  Purchase #4 $202.33   5.363%   $213.181   $213.18   $213.20   $213.20  
  Purchase #5 $213.40   5.732%   $225.6321   $225.63   $225.65   $225.60  
  Purchase #6 $58.48   9.542%   $64.0602   $64.06   $64.05   $64.10  
  Purchase #7 $136.36   13.276%   $154.4632   $154.46   $154.45   $154.50  
  7 purchase totals = $820.14       $888.0856   $888.08   $888.10   $888.10